phpoffice/phpspreadsheet security advisory

CVE-2026-40296: PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer

CVE-2026-40296 is a medium-severity XSS vulnerability in the PHP package phpoffice/phpspreadsheet (CVSS 5.4), published 6 May 2026. The advisory does not name a fixed version. Exploiting it needs a low-privilege user account.

medium 5.4 published 2026-05-06 · updated 2026-10-26

Affected versions: <= 1.30.3
>= 2.0.0, <= 2.1.15
>= 2.2.0, <= 2.4.4
>= 3.3.0, <= 3.10.4
>= 4.0.0, <= 5.6.0
Fixed in: not stated
Newest release: 5.10.0
Severity: Medium · CVSS 5.4
Type: Cross-site scripting (XSS)
CWE-79
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your phpoffice/phpspreadsheet version affected?

Run composer show phpoffice/phpspreadsheet in your project, then enter the version. We check it against this and every other known phpoffice/phpspreadsheet advisory.

Who can exploit CVE-2026-40296

Access: A normal, low-privilege user account in the app.
Interaction: A user also has to do something, such as open a link or a page the attacker prepared.

CVSS vector (scored by GitHub): CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Your app is only exposed if it uses the affected part of phpoffice/phpspreadsheet. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-40296 in phpoffice/phpspreadsheet

Find the installed version: composer show phpoffice/phpspreadsheet. If you never required it yourself, composer why phpoffice/phpspreadsheet shows which package pulls it in.
Update it: composer update phpoffice/phpspreadsheet --with-all-dependencies.
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "phpoffice/phpspreadsheet": "^5.10.0" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-40296.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for XSS issues while the upgrade waits. None of it replaces the fix.

Escape output in your own templates and add a Content-Security-Policy that blocks inline scripts.
Limit who can save the content the advisory names (for example rich text, SVG or form fields).
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-40296 advisory

PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. The HTML writer skips htmlspecialchars escaping when a cell's formatted value differs from the original value. When a cell has a custom number format containing the text placeholder @ along with any additional literal characters (for example ". @", "@ ", or "x@"), the formatter replaces @ with the cell value and adds the extra characters, causing the formatted value to differ from the original and bypassing HTML escaping entirely. An attacker who can control the cell value and number format of an uploaded spreadsheet that is later converted to HTML and displayed to other users can achieve stored cross-site scripting. This issue is fixed in versions 5.7.0, 3.10.5, 2.4.5, 2.1.16, and 1.30.4.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-40296. Advisory title: “PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer”.

References

GitHub advisory GHSA-hrmw-qprp-wgmc github.com

Other phpoffice/phpspreadsheet advisories

Need help patching or upgrading? Laskyr does PHP and Laravel security fixes and upgrades. Tell us what you run and we reply with a plan and a price.

Ask about a fix

Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.